A multi-phase AC power supply system, for example, a three phase AC power supply system typically has three hot or high voltage conductors and a neutral. Three phase power supply systems are used to drive a variety of electrical loads including single phase and three phase electrical loads. Typically, single phase electrical loads are connected across any two active or hot conductors. For a single phase load to function, as desired, it is essential that there be current flowing through both the hot conductors connected to the single phase load.
A brownout condition is an intentional or unintentional drop in voltage in an electrical power supply system. In a three phase AC power supply system, during a brownout condition, only two of the three hot conductors are live or active. In other words, current is available only in two of the hot conductors. If the single phase load happens to be connected to one of the conductors through which there is no current flow, no voltage is supplied thereto which causes the single phase load to malfunction or stop functioning altogether. A brownout condition is different from a blackout or power loss condition. In a blackout condition, current is not available on two or more of the hot conductors and subsequently no voltage is supplied to any single phase electrical load connected thereto. In both instances, the single phase electrical load either malfunctions or stops working.
A brownout typically occurs due to fluctuations or disruptions in the power distribution grid due to environmental interruptions such as storms or insufficient power being generated at a power generation facility. Other environmental conditions such as excessive humidity may also trigger a brownout or under voltage condition. Local and excessive humidity may cause condensation within an electrical panel receiving the three phase AC power supply conductors, leading to a short circuit of a phase which results in lowered voltages being supplied to the electrical loads. Therefore, electrical systems installed in humid areas tend to suffer from such unpredicted or unscheduled brownout conditions on a fairly regular basis.
A brownout condition does not adversely affect three phase loads in that three phase loads do not stop functioning altogether during a brownout condition. A three phase load such as an electric motor will not stop working during a brownout condition. A three phase motor compensates for the loss of current in one of the active conductors connected thereto. Optimal functioning of the motor, during a brownout condition, may be achieved by employing a variable frequency drive (VFD).
It is also known to connect the single phase electrical load between a hot conductor and a neutral of the AC power supply. Problems associated with brownout and blackout conditions described above are encountered in this configuration too.
However, as stated earlier, brownout conditions can be particularly hazardous to the health of the single phase load. For example, if a brownout or power interruption occurs in an electrical system serving, or driving, single phase loads such as ultraviolet (UV) lamps or light emitting diodes (LEDs) and three phase loads such as an electric motor, the single phase loads will stop working or may even fail during the brownout condition. Motors may continue to work at reduced and detrimental speeds if connected to the electrical system through a VFD. Premature mortality of single phase electrical loads during brownout conditions can increase maintenance costs. Stoppage of the single phase electrical loads can inconvenience operating personnel. For example, stoppage of single phase lighting in a control room housing various control modules, during a brownout, can prevent personnel from accessing the various control modules thereby increasing downtime and decreasing efficiency.
In light of the foregoing, a need exists for a reliable system or circuit that can accommodate brownout conditions by continuing to supply standard or normal operating voltages to all single phase electrical loads connected to a three phase AC power supply at all times.